Separation of plutonium and uranium from holder

ABSTRACT

Method of separating plutonium or uranium from a holder, e.g., for facilitating removal of a plutonium or uranium piece from a crucible, by hydriding under a controlled atmosphere at 25* to 100* C.

United States Patent DeGrazio et a].

Feb. 6, 1973 SEPARATION OF PLUTONIUM AND URANIUM FROM HOLDER Inventors: Robert P. DeGrazio, Boulder; Herbert N. Robinson, Denver, both of Colo.

The United States of America as represented by the United States Atomic Energy Commission Filed: May 28, 1971 Appl. No.: 147,901

Assignee:

U.S. Cl. ..75/84.l R, 164/131, 252/301.1 R,

Int. Cl. ..B22d 29/00 Field of Search ..164/131; 264/5; 23/324; 75/84.1 R; 252/30l.1 R

VACUUM [56] References Cited UNITED STATES PATENTS 2,915,362 12/1959 Fried et al. ..23/l4.5 3,279,898 10/1966 Leary et al. ..23/344 Primary Examiner-Carl D. Quarforth Assistant ExaminerB. Hunt AttorneyRoland A. Anderson [57] ABSTRACT Method of separating plutonium or uranium from a holder, e.g., for facilitating removal of a plutonium or uranium piece from a crucible, by hydriding under a 'controlled atmosphere at 25 to 100 C.

6 Claims, 3 Drawing Figures PATENTEDFEB s 1975 3,715,204

IIIIIIIIIIIII ,3 760mm Hg 3 TIIIIIIIIIIIIII'IIIII gen 'fi INVENTOR.

3 ROBERT vF! DE GRAZIO 3 BY HERBERT N. ROBINSON 1 l I I I A Q 200 400 600 800 I000 I200 I400 TEMPERATURE -c /?M SEPARATION OF PLUTONIUM AND URANIUM FROM HOLDER BACKGROUND OF INVENTION In work utilizing plutonium or uranium materials there is sometimes employed a holder or container carrying such material in a molten condition, which upon cooling or solidifying interbonds with walls of the holder. When the holder is of ceramic, such as magnesium oxide, the solidified plutonium or uranium piece may be recovered by breaking away the holder and discarding it. Where, however, a tantalum or the like metal holder is employed the piece has had to be removed by either acid dissolution of the piece, or by melting the piece from the holder. In addition to difficulties and problems of safety and handling connected with dissolution utilizing such as nitric acid and hydrofluoric acid, the time required is objectionable, in some instances being as high as 48 hours. Also, melting or dissolution is objectionable if it is desired to retain the piece in substantially its solid cast or molded form.

SUMMARY OF INVENTION With difficulties and drawbacks such as the foregoing in mind, it is an object of the present invention to provide an improved and relatively simple method for separating the solidified radioactive materials plutonium and uranium from their holders.

Another object of the invention is to provide a method of separating plutonium or uranium pieces from holders which does not require complicated equipment or apparatus to perform.

Various other objects and advantages will appear from the following description and its features.

The invention comprises, in brief, providing a housing about a holder or crucible which carries a plutonium or uranium piece, removing air from within the housing, injecting gaseous hydrogen into the housing and retaining it there for a time for separating the piece from the holder and removing unreacted hydrogen. Sometimes the piece does not immediately drop away from an inverted holder and in that event unreacted hydrogen may be removed from the housing and thereafter a light tap used to accelerate separation.

DESCRIPTION OF DRAWING Various features of the invention are shown in the accompanying drawing, wherein:

FIG. 1 illustrates, more or less diagrammatically, the process and apparatus for performing it;

FIG. 2 shows a modification of the apparatus disclosed in FIG. 1, which may be employed to loosen a' piece from a holder; and

FIG. 3 indicates by graph the general relationship of hydrogen absorption and temperature in connection with the process.

DETAILED DESCRIPTION edge portions of the housing abutting firmly against an annular seal or gasket 7 carried by a cover or base member 8. The housing and cover may be clamped together by appropriate latches 10. The platform 4 may be omitted and the holder with its piece therein placed directly on the bottom of the housing 5.

The interior of the housing 5 communicates through various valves and conduits to tanks, devices or the atmosphere for removing gas from and supplying gas to the interior of the housing, and for conducting various measurements therein. As shown, air or gas may be evacuated from within the housing by pump 1 1 through conduit 13, filter (glass wool) 14 and valve 16. Hydrogen gas, of commercial or other suitable grade, may be supplied from a tank 17 through conduit 18 and valve 19. Conduit 22 and valve 23 may be employed to vent gas or pressure from the interior of the housing to the atmosphere, through a filter (not shown) or otherwise, or to supply a purging gas such as nitrogen or atgon, or mixtures thereof. A manometer or other pressure-vacuum gauge 25 may be coupled to the interior of the housing through conduit 26 and valve 27. A well 31 may be formed to receive a thermometer, thermocouple or other temperature indicator 32. The holder or mold 1 with contained piece 2 may rest in any position on the platform 4, such that hydrogen gas may freely contact it and its piece, the housing being shown propped up by a support member 3 so that as the hydrogen reacts, the piece 2 becomes loose and may drop down onto the platform 4. Platform 4 may be of stainless steel screening. The housing 5 and its cover 8 may be entirely enclosed within glove box or other suitable enclosure, indicated diagrammatically by dotted lines 35, preferably having an inert gas atmosphere such as nitrogen, argon, or the like.

If desired, the various conduits and valves 13-16, 18-19, 22-23, 26-27 may communicate with interior of housing 5 through apertures in cover or base 8.

After a holder 1 with piece 2 therein is housed as indicated by FIG. 1, the housing may be evacuated, preferably to about 15 to 25 inches of mercury (vacuum); and good results have been obtained by about 23 inches of vacuum. After this evacuation hydrogen gas may be supplied from tank 17 to the housing, to a pressure of around 4 to 6 inches of mercury (vacuum) in the housing. Hydrogen reacts with the crucible and with a piece therein, preferable at temperature in the range of about 25 C to C, so that hydrogen is absorbed and the pressure drops; the pressure may be allowed to drop to around 23 inches of mercury (vacuum). If the reaction which takes place does not result in freeing the piece 2 so that it drops by itself onto the platform 4, additional hydrogen may be administered from tank 17 to repeat the operation until the piece is released so as to fall away from the holder. The time at which hydrogen starts to appreciably react with a plutonium or uranium piece and to combine with holder material after admission to the housing, which may be referred to as induction time," generally ranges from immediately up to about 5 minutes. The time from an initial hydrogen admission until piece release has been as low as about 10 minutes, greater time being required of course if a piece does not release with such an initial hydrogen admission and if further admissions are deemed necessary.

In some instances release or drop out of the piece may be facilitated by lightly tapping the holder 1, by a plunger or rod 40 which passes through housing 5 or cover 8 via an appropriate seal or packing 41, as shown in FIG. 2. The holder and its piece 2 may, of course, be tapped by a separate hammer or mallet subsequent to removal of the cover 8 from the housing 5. While it is convenient to have the holder 1 inverted as shown in FIG. 1 such is not essential. It may be upright on member 4 or on the bottom of housing 5, and after being subjected to action of the hydrogen it may be manually inverted to let the piece 2 drop out.

The theory by which a plutonium or uranium piece becomes loosened or released is not fully understood but it is believed that it is as hereinafter brought out. Materials such as tantalum have the property to absorb large quantities of hydrogen, absorption being greater at lower temperatures and decreasing as temperature increases, as indicated by the generally known curve of FIG. 3. As a tantalum holder absorbs hydrogen the specific volume of the tantalum increases, the plutonium or uranium piece tends to at least partially separate from bottom and side walls of the crucible holder, and hydrogen reacts with the material of the piece intermediate contact thereof with bottom and side walls to form hydrides. The layer of hydride at the interface seems to force apart the tantalum and piece so as to dislodge the piece from the holder. That is, it appears that a combination of the holder changing volume and the hydride at the interface cause piece and holder to separate. Scratching or scribing around the joint intermediate the piece and holder seems to hasten or facilitate separation.

If a particularly difficult combination of holder and piece is encountered and such do not separate in response to tapping, some heat may be applied by a heater 34 to facilitate the reaction, but this is not preferred as it is generally desirable to keep to a minimum hydrides which occur when plutonium or uranium is exposed to heat, e.g., as brought out in such as US. Pat. Nos. 2,915,362 and 3,279,898.

Pieces of various initial weights and dimensions have been loosened from their holders by the described method, e.g., plutonium weights of 1,425 grams, 1,070 grams, 800 grams, 600 grams, etc., so that it will be clear that the process is not limited to any particular size or weight of plutonium or uranium piece.

It will be understood that various changes may be made by those skilled in the art within the principles and scope of the invention as brought out in the appended claims.

What is claimed is:

1. The method of separating a tantalum supporting container from a piece of plutonium or uranium which is bonded thereto, which comprises placing said container and piece in an enclosure, at least partially evacuating air from said enclosure, providing a hydrogen gas atmosphere in said enclosure for a period of at least 5 minutes and at a temperature of from about 25 C to about C for subjecting them to the action of said gas and loosening the bond for separation of the piece from the supporting container.

2. The method as claimed in claim 1, wherein said piece comprises plutonium.

3. The method as claimed in claim 1, wherein said provided hydrogen gas atmosphere is at an initial pressure of about 3 pounds per square inch gauge pressure to 17 inches of mercury (vacuum).

4. The method as claimed in claim 1, wherein after a period of about 30 minutes an additional quantity of hydrogen gas is provided in said enclosure.

5. The method as claimed in claim 1, wherein heat is applied to said hydrogen gas atmosphere to raise the temperature above said 25 C.

6. The method as claimed in claim 1, together with the step of tapping said container subsequent to providing said hydrogen gas atmosphere. 

1. The method of separating a tantalum supporting container from a piece of plutonium or uranium which is bonded thereto, which comprises placing said container and piece in an enclosure, at least partially evacuating air from said enclosure, providing a hydrogen gas atmosphere in said enclosure for a period of at least 5 minutes and at a temperature of from about 25* C to about 100* C for subjecting them to the action of said gas and loosening the bond for separation of the piece from the supporting container.
 2. The method as claimed in claim 1, wherein said piece comprises plutonium.
 3. The method as claimed in claim 1, wherein said provided hydrogen gas atmosphere is at an initial pressure of about 3 pounds per square inch gauge pressure to 17 inches of mercury (vacuum).
 4. The method as claimed in claim 1, wherein after a period of about 30 minutes an additional quantity of hydrogen gas is provided in said enclosure.
 5. The method as claimed in claim 1, wherein heat is applied to said hydrogen gas atmosphere to raise the temperature above said 25* C. 